/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 * 
 *  http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.mlizhi.base.codec.net;

import java.io.UnsupportedEncodingException;

import com.mlizhi.base.codec.CharEncoding;
import com.mlizhi.base.codec.DecoderException;
import com.mlizhi.base.codec.EncoderException;
import com.mlizhi.base.codec.StringDecoder;
import com.mlizhi.base.codec.StringEncoder;
import com.mlizhi.base.codec.binary.Base64;


/**
 * <p>
 * Identical to the Base64 encoding defined by <a href="http://www.ietf.org/rfc/rfc1521.txt">RFC
 * 1521</a> and allows a character set to be specified.
 * </p>
 * 
 * <p>
 * <a href="http://www.ietf.org/rfc/rfc1522.txt">RFC 1522</a> describes techniques to allow the encoding of non-ASCII
 * text in various portions of a RFC 822 [2] message header, in a manner which is unlikely to confuse existing message
 * handling software.
 * </p>
 * 
 * @see <a href="http://www.ietf.org/rfc/rfc1522.txt">MIME (Multipurpose Internet Mail Extensions) Part Two: Message
 *  Header Extensions for Non-ASCII Text</a>
 * 
 * @author Apache Software Foundation
 * @since 1.3
 * @version $Id: BCodec.java 797857 2009-07-25 23:43:33Z ggregory $
 */
public class BCodec extends RFC1522Codec implements StringEncoder, StringDecoder {
/**
 * The default charset used for string decoding and encoding.
 */
private final String charset;

/**
 * Default constructor.
 */
public BCodec() {
this(CharEncoding.UTF_8);
}

/**
 * Constructor which allows for the selection of a default charset
 * 
 * @param charset
 *  the default string charset to use.
 * 
 * @see <a href="http://java.sun.com/j2se/1.4.2/docs/api/java/nio/charset/Charset.html">Standard charsets</a>
 */
public BCodec(final String charset) {
super();
this.charset = charset;
}

protected String getEncoding() {
return "B";
}

protected byte[] doEncoding(byte[] bytes) {
if (bytes == null) {
return null;
}
return Base64.encodeBase64(bytes);
}

protected byte[] doDecoding(byte[] bytes) {
if (bytes == null) {
return null;
}
return Base64.decodeBase64(bytes);
}

/**
 * Encodes a string into its Base64 form using the specified charset. Unsafe characters are escaped.
 * 
 * @param value
 *  string to convert to Base64 form
 * @param charset
 *  the charset for <code>value</code>
 * @return Base64 string
 * 
 * @throws EncoderException
 *  thrown if a failure condition is encountered during the encoding process.
 */
public String encode(final String value, final String charset) throws EncoderException {
if (value == null) {
return null;
}
try {
return encodeText(value, charset);
} catch (UnsupportedEncodingException e) {
throw new EncoderException(e.getMessage(), e);
}
}

/**
 * Encodes a string into its Base64 form using the default charset. Unsafe characters are escaped.
 * 
 * @param value
 *  string to convert to Base64 form
 * @return Base64 string
 * 
 * @throws EncoderException
 *  thrown if a failure condition is encountered during the encoding process.
 */
public String encode(String value) throws EncoderException {
if (value == null) {
return null;
}
return encode(value, getDefaultCharset());
}

/**
 * Decodes a Base64 string into its original form. Escaped characters are converted back to their original
 * representation.
 * 
 * @param value
 *Base64 string to convert into its original form
 * @return original string
 * @throws DecoderException
 * A decoder exception is thrown if a failure condition is encountered during the decode process.
 */
public String decode(String value) throws DecoderException {
if (value == null) {
return null;
}
try {
return decodeText(value);
} catch (UnsupportedEncodingException e) {
throw new DecoderException(e.getMessage(), e);
}
}

/**
 * Encodes an object into its Base64 form using the default charset. Unsafe characters are escaped.
 * 
 * @param value
 *  object to convert to Base64 form
 * @return Base64 object
 * 
 * @throws EncoderException
 *  thrown if a failure condition is encountered during the encoding process.
 */
public Object encode(Object value) throws EncoderException {
if (value == null) {
return null;
} else if (value instanceof String) {
return encode((String) value);
} else {
throw new EncoderException("Objects of type " +
  value.getClass().getName() +
  " cannot be encoded using BCodec");
}
}

/**
 * Decodes a Base64 object into its original form. Escaped characters are converted back to their original
 * representation.
 * 
 * @param value
 *  Base64 object to convert into its original form
 * 
 * @return original object
 * 
 * @throws DecoderException
 *  Thrown if the argument is not a <code>String</code>. Thrown if a failure condition is
 *  encountered during the decode process.
 */
public Object decode(Object value) throws DecoderException {
if (value == null) {
return null;
} else if (value instanceof String) {
return decode((String) value);
} else {
throw new DecoderException("Objects of type " +
  value.getClass().getName() +
  " cannot be decoded using BCodec");
}
}

/**
 * The default charset used for string decoding and encoding.
 * 
 * @return the default string charset.
 */
public String getDefaultCharset() {
return this.charset;
}
}
